1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for flow control of a relay in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
An LTE-A system employs new techniques such as carrier aggregation and a relay. The carrier aggregation is used to flexibly extend an available bandwidth. The relay is used to increase a cell coverage and support group mobility and to enable user-centered network deployment.
The relay provides two types of radio interfaces. One is a Uu interface between a relay and a user equipment, and the other is a Un interface between the relay and a base station. A radio bearer is set up in each radio interface. In order for the user equipment to receive a service from the base station via the relay, two radio bearers need to be set up.
In a legacy system not having a relay, only one Uu interface exists as a radio interface, and flow control is not much necessary since a base station (BS) knows all situations.
However, as the relay is employed, it is difficult for the BS to recognize up to a congestion situation, and thus flow control is required.